Discharge lamp modulation system

ABSTRACT

A discharge lamp modulation system in which a signal such as a picture signal is amplitude-modulated or pulsed with a frequency higher than the frequency of the picture signal, and the converted or modulated signal is used to energize a highbrightness discharge lamp such as a xenon discharge lamp for obtaining an optical reproduced signal which is an exact reproduction of the original signal.

United States Patent Inventors Kaoru Sasabe [5 6] References Cited F -Q UNlIED STATES PATENTS $212 Kmmi Mmguch'sh" 2,203,882 6/1940 Shore 178/7.1 A 1 No 784 3,156,826 11/1964 Mutschler 250/199 i l l 1968 3,447,101 5/1969 Gunn-Russell 332/3 la 1971 3,436,472 4/1969 Kyte 178/6.7 Assi nee Mat'suslfim Electric Industrial co ud 3,443,028 5/1969 Pavlik 178/72 2 3,471,701 10/1969 Buenger et al 250/219 v Osaka, Japan Priority Oct. 16, 1967 Primary Examiner-Robert L. Richardson Japan Attorney-Stevens, Davis, Miller & Mosher 42/67093 DISCHARGE LAMP MODULATION SYSTEM 9 Claims, 8 Drawing Figs.

US. Cl 178/6, ABSTRACT: A discharge lamp modulation system in which a 178/66 R, 178/7.6 signal such as a picture signal is amplitude-modulated or Int. Cl H04n 1/22, pulsed with a frequency higher than the frequency of the pic- H04n 1/40 ture signal, and the converted or modulated signal is used to Field of Search 178/6,6.6 energize a high-brightness discharge lamp such as a xenon R, 6.7 R, 6.7 A, 7.1, 7.2, 7.6, DIG. 27; 250/199; discharge lamp for obtaining an optical reproduced signal 332/751, 3 which is an exact reproduction of the original signal.

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INVENTORS HHDRlL /NHBE HIlD /fI lrorgnn BY WMW ATTORNEYS v SHEETSUF 5 PAIENTEUncr 19 Ian km mm a m. mm A a: u WV Q0 o 59% m J E E Q vm M B mm am m? VI m kvfiv kk Q mkm mw m6 MN v MN v m m mm wk m N? \Y lww MAM v QEWQ J mm FL \m m? y 3 m HIROflKI KOTERH DISCHARGE LAMP MODULATION SYSTEM This invention relates to the art of telephotography and more particularly to a discharge tube modulation system for use in telephotography.

An error occurs generally between the waveform of an electrical signal input and the waveform of an optical signal output when a discharge lamp such as a xenon short are lamp or mercury-vapor discharge lamp is employed for the modulation of light. The above error is attributable to the discharge characteristics of the luminous discharge lamp and manifests the defeet that a picture reproduced at the receiver of a facsimile or like system of telephotography involves a tone different from that of the original picture or a tailing, resulting in an undesirable reduction in the quality and property of the reproduced picture.

It is therefore an object of the present invention to obviate the defect described above and to provide a novel and improved modulation system by which a high-fidelity reproduction of an original picture can be effected.

Another object of the present invention is to provide a modulation system of the above character which is adapted for amplitude modulation.

A further object of the present invention is to provide a modulation system of the above character which is adapted for pulse modulation.

A still further object of the present invention is to provide a modulation system which can be utilized in a color facsimile system so that three xenon lamps can be triggered to energize simultaneously by a single manipulation.

The above and other objects, features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an embodiment of the discharge tube modulation system according to the present inventron; I

FIG. 2a and 2b, FIGS. 3a and 3b, and FIGS. 40 through 4d are graphic representations of various waveforms for the illustration of the operation of the system according to the present invention as compared with the operation of a prior art system of this kind;

FIG. 5 is a circuit diagram of another embodiment of the discharge lamp modulation system according to thepresent invention;

FIGS. 6a through 6e are graphic representations of waveforms at various parts of the circuit shown in FIG. 5;

FIG. 7 is a graphic illustration of the operating characteristics of the circuit shown in FIG. 5; and

FIG. 8 is a circuit diagram of a power supply unit in a further embodiment of the discharge lamp modulation system according to the present invention.

Referring first to FIG. 1, an original picture to be transmitted is wrapped around a cylindrical member or revolving drum 1 which is illuminated with light coming from a source of light 2. A photoelectric means 3 is disposed adjacent to the drum 1 so as to receive the light reflected back from a specific point of the original picture carried by the drum 1. The output from the photoelectric means 3 is supplied to a ring modulator 4 for amplitude modulation. The amplitude-modulated signal is transmitted by way of a transmission path 5 which may be a wired path such as a telephone line or a wireless path employ" ing a radio wave in the form of a television signal or stereosignal or an independent radio wave. The signal received at the receiving end is detected by a detector means 6, the detected output delivered from the detector means 6 being supplied to a means 7 which energizes a high-brightness luminous discharge tube 8 such as a xenon lamp while effecting the modulation control of the latter. The optical output from the discharge lamp 8 is passed through an optical system 9 and is reflected by an oscillating mirror 10 to be recorded on a recording sheet 11.

' The system operates in a manner as described below. A signal havinga waveform 3' received by the photoelectric means 3 is amplitude-modulated by the ring modulator 4 to appear as a waveform 4' which is then sent to the receiving end by way of the transmission path 5. At the receiving end, the signal is detected by the detector means 6 to appear as a detected output having a waveform 6', and the detected output drives the means 7 to energize the high-brightness luminous discharge lamp 8 to effect the modulation control thereof. The optical output 8' delivered from the discharge lamp 8 is proportional to the output waveform 6' delivered from the detector means 6 and has an envelope which coincides with the waveform 3'. The optical output 8' from the discharge lamp 8 is passed through the optical system 9 and is reflected by the oscillating mirror 10 to produce a spot 12 on the recording sheet 11 at a position corresponding to a point on the original picture to be transmitted. The oscillating mirror 10 is caused to oscillate in one direction and another in synchronism with one revolution of the drum so that the moving beam of light can sweep across the recording sheet II in exact coincidence with the subscanning speed at the transmitter. Thus, the original picture can exactly be reproduced on the recording sheet I l.

The chief aim of the present invention is to have an exactly and directly proportional relationship between the waveform 3' and the envelope of the optical output 8' from the highbrightness luminous discharge lamp 8.

How the above aim is attained by the present invention will be described with reference to'FIGS. 2 to 4. Suppose that the input has a waveform as shown in FIG. 2a. Then, the optical output from the discharge lamp such as a xenon discharge lamp has a waveform as shown in FIG. 21;. That is, the optical output has such a nature that an abrupt luminescence takes place at the rising portion of a waveform with which luminescence should persist over a certain period, and the Iuminescence decreases transiently in about 20 msec. and does not show any appreciable increase thereafter. The waveform seen in FIG. 2b differs conspicuously from the transmitted waveform seen in FIG. 2a and can not therefore be used in the existing form.

A method for overcoming the above drawback is shown in FIG. 3. In FIG. 3b it will be seen that the resultant waveform is free from an abrupt change in its rising portion which is sufficiently made dull. Thus, the undesirable rising characteristic seen in FIG. 2b can be obviated and the reduction in the vicinity of 20 msec. is not so appreciable. However, this method has the disadvantage of reducing the high-frequency components of an original picture to be transmitted, which is followed by deterioration of the resolution.

The present invention overcoming the prior defect proposes a novel method according to which a waveform as shown in FIG. 4a is subjected to modulation by a carrier wave, and the carrier wave which is left to give a waveform as shown in FIG. 4b or 4c is used to energize a discharge lamp such as a xenon discharge lamp so as to obtain an output which takes the waveform of FIG. 40 again. This method is advantageous in that any reduction in the optical output at its rising portion as seen in FIG. 2b does not occur. Since the luminescent characteristic of the lamp can be fully developed and steep pulses of light can thereby be obtained, the quantity of the optical output does not show an appreciable reduction even though the carrier wave is left in the signal. Furthermore, any practical inconvenience would not be caused when the carrier wave is selected to have a frequency such that there are more than l0 pulses per mm. of a reproduced picture.

It will be appreciated that, according to the present invention, no substantial error in waveform does exist between an electrical signal input and an optical signal output and the reproduced picture is excellent in quality and property. Furthermore, an oscillating mirror system having a reflecting plate of small area can be employed in the present invention which permits the use of a high-brightness discharge tube. This leads to the advantage that a color film having a low sensitivity can satisfactorily be used in telephotography.

Referring to FIG. 5 showing another embodiment of the present invention, the system comprises a DC power supply 13, a high-voltage generator means 14 for igniting a lamp, a relay 16, an arc discharge luminous lamp 17 such as a xenon lamp connected to the high-voltage generator means 14, and a variable resistor 20 connected at one of its terminals with the luminous lamp 17 through a resistor 18. The other terminal of the variable resistor 20 is grounded. A switch 19 is connected in parallel with the variable resistor 20. The switch 19 is connected mechanically through the relay 16 with a starting switch for the high-voltage generator means 14 for interlocked operation with the starting switch 15. The system comprises further a transistor 21 connected in parallel with the variable resistor 20, a signal input terminal 22, a sawtooth waveform generator or triangular waveform generator 27, an adder 23 for adding the signal from the sawtooth waveform generator 27 to a signal supplied tothe input terminal 22, a variable resistor 25 connected in parallel with a DC power supply 26, and a resistor 24 connected between the variable resistor 25 and the adder 23. A slicer 28 is connected with the adder 23 for slicing the output from the adder 23. A wave shaper 29 is connected with the slicer 28 and its output is supplied to the base of the transistor 21.

The circuit shown in FIG. 5 operates in a manner as,

described below. A signal having a waveform as, for example, shown in FIG. 6a appearing at the input terminal 22 is supplied to theadder 23 where the signal is added to the output from the sawtooth waveform generator 27, which has a waveform as shown in FIG. 6b, so that a signal having a waveform as shown in FIG. 6c is thereby obtained. In FIG. 6c, E represents the DC bias applied by the DC power supply 26. In the slicer 28, the signal shown in FIG. 6 c is sliced at levels I5. andE 'The sliced signal is subjected to wave shaping in the wave shaper 29 to appear as a pulse-width modulated signal having a waveform as shown in FIG. 6d, which is supplied to the base of the transistor 21. The transistor 21 conducts in response to the pulses existing in the signal and is cut off in response to the absence of the pulses.

When now the starting switch 15 is urged to its closed position, a high-voltage generated by the high-voltage generator means 14 is applied to the discharge lamp 17, and at the same time, the relay 16 is energized to urge the switch 19 to its closed position. Consider the case in which the transistor 21 is not present. Then, the current for the discharge lamp 17 is solely limited by the resistor 18 so that a large starting current is supplied to the discharge lamp 17 to initiate an arc discharge in the lamp 17. In response to the arc discharge taking place in the discharge lamp 17, the relay 16 is deenergized to open the switch 19. As a result, a series circuit of the resistors l8 and limits now the current to be supplied to the discharge lamp 17 whose discharge current is thereby reduced. A bright luminescence occurs in the discharge lamp 17 when the resistor 20 is short-circuited thereacross, while a dark luminescence occurs in the discharge lamp 17 when the resistor 20 is not short-circuited thereacross.

Consider now the switching operation of the transistor 21 which takes place in response to application of the signal waveform shown in FIG. 6d. A bright or dark luminescence occurs in the discharge lamp 17 depending on the width of pulses in the signal, and the discharge lamp l7 delivers an optical output which is modulated accordingly as seen in FIG. 6e. It is thus possible to effect a high-fidelity reproduction of an original picture in the manner similar to that described with reference to FIG. 4.

The discharge lamp 17 requires a minimum holding current in order that its luminous state can be sustained, and any reduction in the discharge current from the minimum results in arc extension whereby modulation is ceased. Therefore, I, must naturally be larger than the holding current, but an excessive increase in the value of I, is undesirable since the degree of modulation of light is thereby reduced. Further, the luminous discharge at a low current density in the vicinity of the holding current is generally unstable, and persistence of such an unstable state for a long period of time may sometimes result in extinction of the arc. Because of the above fact, persistence of a no-signal state as shown by a period p-q in FIG. 6a has been undesirable in a conventional system of amplitude modulation, since the arc becomes unstable during this period. A suitable means for stabilizing the circuit is inevitably required in the conventional system in order to continuously effect a stable discharge.

In contrast to the conventional system, the embodiment of the present invention shown in FIG. 5 comprises a means for applying a suitable bias E, as seen in FIG. 6c, whereby to adjust the slicing levels E, and B, so that the tip portions of the FIG. 7 shows the discharge current-discharge voltage 7 sawtooth waveform can be sliced even in the absence of any signal and a pulse current consisting of a train of slender pulses having the repetition period T of the sawtooth waveform can continuously flow across the discharge lamp 17 during the no-signal period p-q. According to the invention, the luminous discharge can remarkably be stabilized since the discharge lamp 17 is energized by the slender pulses as well as by the DC component even in the no-signal period. By suitably selecting the pulse width t and period T, it is possible to reduce the DC component I, for. sustaining the discharge and the luminescence can stably be maintained without substantially the aid of the DC component. In such a case, the DC component I, can be regulated by the variable resistor 20 in FIG. 5. The embodiment shown in FIG. 5 is further advantageous in that a saving in the power consumption in the section including the transistor 21 can be realized since the transistor 21 participates only in the switching operation.

Referring toFIG. 8, a power supply unit for three discharge lamps which can be utilized in a color facsimile system will be described. The power supply unit comprises a plug 30 connectable with a commercial power supply. The plug 30 is connected through a fuse 31 and a switch 32 with a rectifier circuit 33 for obtaining a DC output and further through a switch 34 with a transformer 35. An airgap 36 is disposed in parallel with the secondary winding of the transformer 35. A series circuit including a capacitor 37 and the primary windings of transfonners 38, 39 and 40 is connected in series with the secondary winding of the transformer 35. The secondary windings of the transformers 38, 39 and 40 are connected at one terminal thereof with one terminal of respective discharge lamps 41, 42 and 43, while these secondary windings are connected at the other terminal thereof with a common terminal 44 which is connected with a movable blade of a switch 45. The switch 45 has two stationary contacts b and m, the latter contact m being connected with the output terminal of the rectifier circuit 33. The switch 45 takes normally such a position that the movable blade is urged to contact the stationary contact m by a spring, but the movable blade is urged into contact with the other stationary contact b when a current flows across a coil 46. Many switches of similar structure appearing in the later description are operative in the same manner as switch 45.

The discharge lamps 41, 42 and 43 are grounded at the other terminal thereof through respective series circuits of resistors 47, 48; 49, 50; and 51, 52. Transistors 53, 54 and 55 are connected in parallel with the respective resistors 48, 50 and 52. Modulated red, blue and green signals are supplied to terminals 56, 57 and 58 connected to the bases of the transistors 48, 50 and 52, respectively. These signals have a waveform as shown in FIG. 6d. The connection point between the resistors 47 and 48 is connected directly to a stationary contact m of a switch 59, the connection point between the resistors 49 and 50 to a stationary contact m of a switch 60, and the connection point between the resistors 51 and 52 to a stationary contact m of a switch 61. The other stationary contacts b of all these switches 59, 60 and 61 are in the open position and their movable blades are grounded. The contact m of the switch 59 is further connected with the tenninal 44. A stationary contact b of a switch 62 is connected with the terminal 44. The switch 62 has its movable blade connected with a stationary contact b of a switch 63, which has its movable blade connected with a stationary contact b of a switch 64. The other stationary contacts m of all these switches 62, 63 and 64 are in their open positions. Driving coils 65, 66 and 67 are associated with the sets of switches 62, 59; 63, 60; and 64, 61, respectively. These coils 65, 66 and 67 are grounded at one terminal thereof and are connected at the other terminal thereof with the other terminal of the respective discharge lamps 41, 42 and 43.

The terminal 44 is further connected with a stationary contact m of a switch 68 which has its movable blade connected with capacitors 71 and 72 through respective resistors 69 and 70. The capacitors 71 and 72 are grounded at the other terminal thereof. A series circuit of a resistor 73 and a coil 74 is connected in parallel with the capacitor 71, while the coil 46 is connected in parallel with the capacitor 72. The coil 74 is arranged to drive the switch 34 so that the switch 34 can be changed over in response to a flow of driving current through the coil 74. A resistor 76 is connected in series with a driving coil 75 for the switch 68, and the series circuit of the resistor 76 and the coil 75 is connected in parallel with a capacitor 77. The capacitor 77 is grounded at one terminal thereof and is connected at the other terminal thereof with the movable blade of the switch 64 through a resistor 78. Since the time constant circuit consisting of the resistor 70 and the capacitor 72 has a relatively large time constant, a relatively long time T is required before the switch 45 is changed over after driving current starts to flow through the coil 46. However, the switches 34 and 68 are adapted to be changed over with a time shorter than the time T. Alternatively, the elements 69, 71, 73, 74 and others may be, suitably selected and combined with one another so that the movable blade of the switch 34 can be urged and kept in contact with the stationary contact b for only a fixed period shorter than T after a voltage is applied to the terminal 44.

The circuit shown in FIG. 8 operates in a manner as described below. When the switch 32 is closed, a voltage rectified by the rectifier circuit 33 appears at the terminal 44. This voltage is applied across the switch 68 to supply a driving current through the coils 46 and 74. The driving current flows quickly through the coil 74 thereby to close the switch 34. The closure of the switch 34 energizes the transformer 35 with the result that a high-frequency discharge takes place across the airgap 36 thereby energizing the transformers 38, 39 and 40 through the capacitor 37 and generating a high voltage of the order of several kv., across the secondary windings of these transformers. As a result, the discharge lamps 41, 42 and 43 are energized simultaneously. At the beginning of the discharge, the resistors 48, 50 and 52 having a high resistance are short-circuited by the action of the respective switches 59, 60 and 61 so that a large current is supplied to the discharge lamps 41, 42 and 43. After these discharge lamps 41, 42 and 43 have been energized, the coils 65, 66 and 67 are excited due to an increase in the terminal voltage of the resistors 47, 49 and 51, and the switches 62, 63, 64, 59, 60 and 61 are thereby changed over from the previous position. As a result, the resistors 48, 50 and 52 are released from the state of shortcircuit thereacross. Accordingly, the short-circuit of the resisters 48, 50 and 52 is henceforth controlled by the on-off of the transistors 53, 54 and 55 in response to the appearance of the pulse signals at the terminals 56, 57 and 58, with the result that modulated light is emitted from the discharge lamps 41, 42 and 43.

By the way, when the discharge lamps 41, 42 and 43 are energized and the switches 62, 63 and 64 are changed over thereafter, a driving current flows through the coil '75 in a delayed relation which is dependent upon the combination of the resistor 78 and the capacitor 77, thereby urging the switch 68 to its open position. As a result, no current flows through the coil 74, thereby urging the switch 34 to its open position, ceasing the generation of high voltage and giving rise to a steady state. The time required for this operation is shorter than the time T which depends on the delaying action imparted by the combination of the resistor 70 and the capacitor 72, and therefore the switch 45 is prevented from going into its open position.

Consider now a case in which at least one of the discharge lamps 41, 42 and 43 fails to be energized. Suppose, for example, that the discharge lamp 42 fails to be energized. In such a case, the coil 66 alone is not excited and no change-over takes place in the switches 63 and 60. Since, therefore, the coii 75 is not excited and the switch 68 is not urged to its open position, exciting current flows through the coil 46 after a predetermined time, thereby urging the switch 45 to its open position. As a result, no voltage appears at the terminal 44, no exciting current flows through the coils 74 and 46, and the system is restored to its original state and is kept in such a state until voltage appears again at the terminal 44. An operation similar to the above is repeated until finally all the discharge lamps 41, 42 and 43 are energized. In this manner, the closure of the switch 32 can automatically initiate simultaneous energization of all the discharge lamps 41, 42 and 43.

What is claimed is:

1. An electrical discharge modulation system, comprising a high-brightness discharge lamp; means maintaining said discharge lamp in a preliminary discharge state, including means for supplying a discharge sustaining current to said discharge lamp; means for sampling an input signal having a varying amplitude including means for generating a sampling signal having a frequency higher than the frequency of said input signal; means forming a pulse signal-representative of the sampled amplitudes of said input signal; and means employing said pulse signal for lighting said discharge lamp for pulse widths substantially equal to that of said pulse signal.

2. An electrical discharge modulation system according to claim 1, wherein said pulse signal forming means comprises means for amplitude modulating, by said input signal, a carrier signal of a higher frequency than that of said input signal, and means forming said pulse signal from the resulting amplitude modulated signal.

3. An electrical discharge modulation system according to claim 1, wherein said pulse signal forming means comprises means for pulse width modulating a carrier signal modulated by said input signal.

4. An electrical discharge modulation system according to claim 1, further comprising means for maintaining said discharge sustaining current at a relatively low value and means for stabilizing the maintenance of a preliminary discharge in the absence of an input signal, including means exciting said discharge lamp with a sequence of pulses of relatively small pulse width.

5. A discharge lamp modulation system comprising a revolving drum having an original picture to be transmitted wrapped around the surface thereof, a light source for directing a beam of light to said drum, photoelectric means for receiving the light reflected back from said original picture carried by said drum, means for amplitude modulating, by the output of said photoelectric means, a carrier signal of a frequency higher than the frequency of said output, means for detecting the output of said modulating means, a highbrightness discharge lamp energized by the output from said detector means, an oscillating mirror for receiving the light emerging from said discharge lamp, and a recording sheet for recording the light reflected from said oscillating mirror.

6. An electrical discharge lamp modulation system comprising a high-brightness discharge lamp; means for supplying a discharge sustaining current to said lamp, including a DC power source connected to one terminal of said lamp; means for applying a high voltage to said lamp for lighting it, includswitch for initiating the operation of said lamp; relay means urged with the operation of said starting switch to close said switch means-means for pulse width modulating a carrier signal modulated by said input signal at a frequency higher than that of said input signal; and means for applying the resulting pulse width modulated signal to the base of said switching transistor.

7. A discharge lamp modulation system, comprising a plurality of high-brightness discharge lamps; pulse signal forming means controlling the lighting state of said respective lamps, including means for sampling respective input signals at a repetition rate higher than the frequencies of said input signals; means for generating a discharge sustaining voltage on the connection of said system with a power supply; means for applying a starting high voltage to said lamps on the connection of said system with said power supply; means preventing subsequent generation of said starting high voltage when all of said lamps have been ignited, including means for controlling said high voltage applying means; and means for deenergizing said ignited lamps when at least one of said lamps fails to become ignited, said deenergizing means generating a further starting high voltage.

8. A discharge lamp modulation system comprising a plurality of high-brightness discharge lamps, means for sampling the respective input signals at a repetition rate higher than the frequencies of said input sign air; and forming respective corresponding pulse signals to thereby control the respective lighting states of said lamps, means for imparting a discharge sustaining voltage to said lamps on the connection of the system with a power supply, means for applying a starting high voltage to said lamp, means operative by detecting the generation of said discharge sustaining voltage to set said high voltage applying means enable to ignite all the lamps simultaneously, means for temporarily preventing the discharge sustaining voltage from being imparted to said sustaining voltage de' tection means by detecting the nonignition of at least one of said lamps, and means for ceasing the operation of said high voltage applying means by sensing the ignition of all the lamps.

9. An electrical discharge modulation system, comprising a high-brightness discharge lamp; means maintaining said discharge lamp in a preliminary discharge state, including means for supplying a discharge sustaining current to said discharge lamp; means for pulse width modulating a carrier signal modulated by an input signal, including means for sam pling said modulated carrier signal at a repetition rate higher than the frequency of said input signal; and means employing said pulse signal for lighting said discharge lamp for pulse widths substantially equal to that of said pulse signal; wherein said pulse width modulation means comprises means for superposing upon said input signal a sawtooth waveform signal of a frequency higher than that of said input signal, and means for slicing the resulting superposed signal at a signal level beneath the apex of said sawtooth signal. 

1. An electrical discharge modulation system, comprising a highbrightness discharge lamp; means maintaining said discharge lamp in a preliminary discharge state, including means for supplying a discharge sustaining current to said discharge lamp; means for sampling an input signal having a varying amplitude including means for generating a sampling signal having a frequency higher than the frequency of said input signal; means forming a pulse signal representative of the sampled amplitudes of said input signal; and means employing said pulse signal for lighting said discharge lamp for pulse widths substantially equal to that of said pulse signal.
 2. An electrical discharge modulation system according to claim 1, wherein said pulse signal forming means comprises means for amplitude modulating, by said input signal, a carrier signal of a higher frequency than that of said input signal, and means forming said pulse signal from the resulting amplitude modulated signal.
 3. An electrical discharge modulation system according to claim 1, wherein said pulse signal forming means comprises means for pulse width modulating a carrier signal modulated by said input signal.
 4. An electrical discharge modulation system according to claim 1, further comprising means for maintaining said discharge sustaining current at a relatively low value and means for stabilizing the maintenance of a preliminary discharge in the absence of an input signal, including means exciting said discharge lamp with a sequence of pulses of relatively small pulse width.
 5. A discharge lamp modulation system comprising a revolving drum having an original picture to be transmitted wrapped around the surface thereof, a light source for directing a beam of light to said drum, photoelectric means for receiving the light reflected back from said original picture carried by said drum, means for amplitude modulating, by the output of said photoelectric means, a carrier signal of a frequency higher than the frequency of said output, means for detecting the output of said modulating means, a high-brightness discharge lamp energized by the output from said detector means, an oscillating mirror for receiving the light emerging from said discharge lamp, and a recording sheet for recording the light reflected from said oscillating mirror.
 6. An electrical discharge lamp modulation system comprising a high-brightness discharge lamp; means for supplying a discharge sustaining current to said lamp, including a DC power source connected to one terminal of said lamp; means for applying a high voltage to said lamp for lighting it, including a high-voltage generator connected to said one terminal, at least one resistor connected between ground and the other terminal of said lamp, switch means and a switching transistor respectively connected in parallel with said resistor, a starting switch for initiating the operation of said lamp; relay means urged with the operation of said starting switch to close said switch means; means for pulse width modulating a carrier signal modulated by said input signal at a frequency higher than that of said input signal; and means for applying the resulting pulse width modulated signal to the base of said switching transistor.
 7. A discharge lamp modulation system, comprising a plurality of high-brightness discharge lamps; pulse signal forming means controlling the lighting state of said respective lamps, including means for sampling respective input signals at a repetition rate higher than the frequencies of said input signals; means for generating a discharge sustaining voltage on the connection of said SYSTEM with a power supply; means for applying a starting high voltage to said lamps on the connection of said system with said power supply; means preventing subsequent generation of said starting high voltage when all of said lamps have been ignited, including means for controlling said high voltage applying means; and means for deenergizing said ignited lamps when at least one of said lamps fails to become ignited, said deenergizing means generating a further starting high voltage.
 8. A discharge lamp modulation system comprising a plurality of high-brightness discharge lamps, means for sampling the respective input signals at a repetition rate higher than the frequencies of said input signals and forming respective corresponding pulse signals to thereby control the respective lighting states of said lamps, means for imparting a discharge sustaining voltage to said lamps on the connection of the system with a power supply, means for applying a starting high voltage to said lamp, means operative by detecting the generation of said discharge sustaining voltage to set said high voltage applying means enable to ignite all the lamps simultaneously, means for temporarily preventing the discharge sustaining voltage from being imparted to said sustaining voltage detection means by detecting the nonignition of at least one of said lamps, and means for ceasing the operation of said high voltage applying means by sensing the ignition of all the lamps.
 9. An electrical discharge modulation system, comprising a high-brightness discharge lamp; means maintaining said discharge lamp in a preliminary discharge state, including means for supplying a discharge sustaining current to said discharge lamp; means for pulse width modulating a carrier signal modulated by an input signal, including means for sampling said modulated carrier signal at a repetition rate higher than the frequency of said input signal; and means employing said pulse signal for lighting said discharge lamp for pulse widths substantially equal to that of said pulse signal; wherein said pulse width modulation means comprises means for superposing upon said input signal a sawtooth waveform signal of a frequency higher than that of said input signal, and means for slicing the resulting superposed signal at a signal level beneath the apex of said sawtooth signal. 